Cyanates and thiocyanates as activators for heavy-metal-free emulsion polymerization systems



Patented June 29, 1954 CYANATES AND THIOCYANATES AS ACTIVA- TORS FORHEAVY-METAL-FREE EMUL- SION POLYMERIZATION SYSTEMS Willard M. St. John,Jr., Borger, Tex., assignor to Phillips Petroleum Company, a corporationof Delaware No Drawing. Application November 20, 1950,

Serial No. 196,717

(c1. ze -84.3)

17 Claims. 1

This invention relates to the polymerization of unsaturated organiccompounds while dispersed in an aqueous emulsion. In some of itspreferred aspects the invention relates. to the employment of novelreductants in conjunction with certain hydroperoxides in recipes used atmoderately low polymerization temperatures for effecting production ofsynthetic rubber by emulsion polymerization of conjugated diolefins.

Numerous recipes have been developed for carrying out emulsionpolymerization reactions especially at sub-atmospheric temperatures.Highly activated recipes, such as those of the redox type, have beenfrequently employed. The materials which have been suggested asoxidizing and reducing components in redox emulsion polymerizationsystems are numerous and varied. Heavy metal salts, such as solubleferrous salts, have been employed as reductants and among theoxygen-giving materials such compounds as persulfates and peroxides arewell known. It is also frequently preferred to include an organicreducing agent such as a sugar or other readily oxidizable polyhydroxycompound in the polymerization recipe although in many instancessatisfactory results are realized in the absence of this component.

An object of this invention is to effect polymerization of organiccompounds in aqueous emulsion. Another object of the invention is toprovide a new type of recipe for the emulsion polymerization ofconjugated diolefins, at moderately low temperatures. A further objectis to polymerize conjugated diolefins in aqueous emulsion to producesynthetic rubbers, using a recipe free from deliberately added heavymetal compounds. Yet another object is to effect such polymerization inthe absence of sugars. A further object is to provide new activatorsuseful in emulsion polymerization of. unsaturated organic compounds.Other objects and advantages of the invention will be apparent, to oneskilled in the art, from the accompanying disclosure and discussion.

I have now discovered a method for effecting emulsion polymerizationreactions whereby cyanates or thiocyanates are employed as activators,or reductants, together with hydroperoxides as oxidants to producepolymers that are essentially free from heavy metals. The compoundswhich are applicable can be represented by the formula MCNX where Mrepresents an alkali metal or ammonium and X represents oxygen orsulfur. Compounds which are most generally preferred are the cyanatesand thiocyanates of sodium and potassium and particularly thesulfur-containing compounds of these metals, i. e. KCNS and NaCNS. Theoxidizing components used in my preferred recipes are trisubstitutedhydroperoxy- 2 methanes, generally containing not more than 30 carbonatoms per molecule.

The oxidizing components used in these recipes are organichydroperoxides, and are preferably trisubstituted hydroperoxymethanes.The latter compounds are represented by the formula:

wherein each X, individually, is one of the group consisting ofaliphatic, cycloaliphatic, aromatic, olefinic, and cycloolefinicradicals. Each of these radicals can be completely hydrocarbon incharacter, and can be of mixed character such as aralkyl, alkaryl, andthe like, and can also have non-hydrocarbon substituents; particularlyuseful non-hydrocarbon substituents include oxygen in the form ofhydroxy and ether compounds, sulfur in similar compounds (1. e. mercaptocompounds and thioethers) and halogen compounds. Such hydroperoxides canbe easily prepared by simple oxidation, with free oxygen, of thecorresponding hydrocarbon or hydrocarbon derivative, i. e. of the parenttrisubstituted methane. If desired the hydroperoxides can be used in theform of their alkali metal salts. Among the preferred trisubstitutedhydroperoxy methanes are those containing from 10 to 30 carbon atoms permolecule, as disclosed and claimed in copending application Serial No.107,638 filed July 29, 1949. Further examples of suitable hydroperoxideswhich can be used are: trialkyl hydroperoxymethane having from 6 to 9carbon atoms per molecule, alkenyl trisubstituted hydroperoxymethaneshaving from 6 to 30 carbon atoms, hydroperoxides ofoctahydrophenanthrene and its derivatives, hydroperoxides of alkyltetralins and their derivatives, aryl cyclohexyl hydroperoxides,tertiary butyl hydroperoxide.

In the polymerization systems of this invention, the thiocyanates andcyanates appear to act as reductants and/or activators. No otheractivating ingredients, such as compounds of polyvalent-multivalentmetals, need be added in order to obtain satisfactory and rapidpolymerization of the monomeric material, even at subatmospheric (butabove freezing) temperatures, except as such compounds may fortuitouslybe present as traces in the polymerization mixture. Similarly, no otherreducing ingredient, such as a reducing sugar, need be added.

The amount of the said activator compound used to obtain optimum resultsis dependent upon other ingredients in the recipe. The amount of thecyanate or thiocyanate used will generally be in the range from 0.02 to2 parts by weight (0.25 to 20 millimols) per parts of monomeric materialwith 0.04 to 1.2 parts (0.5 to 15 millimols) being most generallypreferred.

The amount of hydroperoxymethane used to obtain an optimum reaction ratewill depend upon the polymerization recipe used and upon the reactionconditions. The amount is generally expressed in millimols per 100 partsof monomeric material, using in each instance the same units of weightthroughout, i. e. when the monomeric material is measured in pounds thehydroperoxymethane is measured in millipound mole. The same is true forother ingredients in the polymerization recipe. The amount ofhydroperoxymethane will usually be in the range from 0.25 to 10millimols per 100 parts of monomeric material.

The ratio of hydroperoxide to cyanate or thiocyanate, expressed inmillimols, will usually be in the range from 1:1 to 2:1. It isordinarily preferred to employ at least a slight molar excess of thehydroperoxide.

One of the advantages of the polymerization recipes, as disclosedherein, is that they are applicable for use in the production of highsolids latices, i. e. latices resulting from the use of a smaller amountof aqueous medium and emulsifier than is generally used in conventionalpolymerization procedures. For this type of operation the Weight ratioof aqueous phase to monomeric material will generally be in the rangefrom 0.5:1 to 1:1 and the extent of conversion will generally range from70 per cent to substantially complete conversion.

Emulsifying agents which are applicable in these polymerizations arematerials such as potassium laurate, potassium oleate, and the like, andsalts of rosin acids. Particularly useful are the specific mixtures ofsalts of fatty acids and of rosin acids, which seem to have asynergistic action when used with some of these same hydroperoxides, asmore fully disclosed and claimed by Charles F. Fryling and Archie E.Follett in their application Serial No. 72,534, filed January 24., 1949.However, other emulsifying agents, such as ncnionic emulsifying agents,salts of alkyl aromatic sulfonic acids, salts of alkyl sulfates, and thelike which will produce favorable results under the conditions of thereaction, can also be used in practicing the invention, either alone orin admixture with soaps. The amount and kind of emulsifier used toobtain optimum results is somewhat dependent upon the relative amountsof monomeric material and aqueous phase, the reaction temperature, andthe other ingredients of the polymerization mixture. Usually an amountbetween about 0.3 and 5 parts by weight per 100 parts of monomericmaterial will be found to be sufiicient.

The pH of the aqueous phase can be varied over a fairly wide rangewithout producing unduly deleterious effects on the conversion rate orthe properties of the polymer. In general the pH is preferably at least9, and usually is within the range of 9.0 to 12.0.

When carrying out polymerization reactions according to the process ofthis invention, it is frequently considered desirable to include anelectrolyte in the system, such as potassium chloride, trisodiumphosphate, or other salt which will not produce deleterious efi'ects.One function of an electrolyte is to increase the fluidity of the latex,and it also reduces precoagulation. Generally the amount of such saltwill not exceed one part by weight per 100 parts of monomers.

I generally use the cyanates and thiocyanates discussed herein asactivators in polymerization recipes at polymerization temperatures from4 about 30 0. down to 0 C. However, temperatures as high as C. or evenhigher can be employed if desired.

In effecting emulsion polymerization of a monomeric material,particularly when a batchtype or semi-batch-type operation is carriedout, the reactor is usually first charged with the aqueous medium, whichcontains the desired emulsifying agent, and the monomeric material isthen admixed with agitation of the contents. At the same time a reactionmodifier, such as a mercaptan, is also included, usually in solution inat least a part of the monomeric material. An activator solution and anoxidant are separately added to the reaction mixture, and reaction thenproceeds. A preferred manner of adding these two constituents is usuallyto have the activator solution incorporated in the aqueous medium priorto addition of the monomeric material, and to add the oxidant as thelast ingredient. Sometimes, however, satisfactory polymerization resultscan be obtained when this procedure is reversed. It is also sometimesthe practice to add portions of one or the other of the activatorsolutions and oxidant intermittently, or continuously, during the courseof the reaction. If the operation is carried out continuously, streamsof the various ingredients are admixed in somewhat the same order priorto their final introduction into the polymerization reaction zone.

The monomeric material polymerized to produce polymers by the process ofthis invention comprises unsaturated organic compounds which generallycontain the characteristic structure CH2=C and, in most cases, have atleast one of the disconnected valences attached to an electronegativegroup, that is, a group which increases the polar character of themolecule such as a chlorine group or an organic group containing adouble or triple bond such as vinyl, phenyl, cyano, carboxy or the like.Included in this class of monomers are the conjugated butadienes or1,3-butadienes such as butadiene (1,3-butadiene),2,3-dimethyl-1,3-butadiene, isoprene, piperylene, 3 furyl 1,3 butadiene,3 methoxy 1,3- butadiene and the like; haloprenes, such as chloroprene(2 chloro 1,3 butadiene), bromoprene, methylchloroprene(2-chloro-3-methyl- 1,3-butadiene), and the like; aryl olefins such asstyrene, various alkyl styrenes, p-chlorostyrene, p-methoxystyrene,alpha-methylstyrene, vinylnaphthalene and similar derivatives thereof,and the like; acrylic and substituted acrylic acids and their esters,nitriles and amides such as acrylic acid, methacrylic acid, methylacrylate, ethyl acrylate, methyl alpha-chloroacrylate, methylmethacrylate, ethyl methacrylate, butyl methacrylate, methylethacrylate, acrylonitrile, methacrylonitrile, methacrylamide and thelike, methyl isopropenyl ketone, methyl vinyl ketone, methyl vinylether, vinylethinyl alkyl carbinols, vinyl acetate, vinyl chloride,vinylidene chloride, vinylfurane, vinylcarbazole, vinylacetylene andother unsaturated hydrocarbons, esters, alcohols, acids, ethers, etc.,of the types described. Such unsaturated compounds can be polymerizedalone, in which case simple linear polymers are formed, or mixtures oftwo or more of such compounds which are copolymerizable with each otherin aqueous emulsion can be polymerized to form linear copolymers.

The process of this invention is particularly efiective when themonomeric material polymerized is a polymerizable aliphatic conjugateddiolefin or a mixture of such a conjugated diolefin with lesser amountsof one or more other compounds containing an active CH2=C group whichare copolymerizable therewith such as aryl olefins, acrylic andsubstituted acrylic acids, esters, nitriles and amides, methylisopropenyl ketone, vinyl chloride, and similar compounds mentionedhereinabove. In this case the products of the polymerization are highmolecular weight linear polymers and copolymers which are rubbery incharacter and may be called synthetic rubber. Often preferred asreactants are conjugated dienes having not more than six carbon atomsper molecule. Although, as can-be readily deduced from the foregoing,there is a host of possible reactants, the most readily and commerciallyavailable monomers at present, are butadiene itself (1,3-butadiene) andstyrene. The invention will, therefore, be more particularly discussedand exemplified with reference to these typical reactants. With thesespecific monomers, it is usually preferred to use them together, inrelative ratios of butadiene to styrene between 65:35 and 90:10 byweight.

It is generally preferred that the emulsion be of an oil in water type,with the ratio of aqueous medium to monomeric material between about0.5: 1 and about 2.75:1, in parts by weight. In the practice of theinvention suitable means will be necessary to establish and maintain anemulsion and to remove reaction heat to maintain a desired reactiontemperature. The polymerization can be conducted in batches,semicontinuously, or continuously. The total pressure on the reactantsis preferably at least as great as the total vapor pressure of themixture, so that the initial reactants will be present in liquid phase.Usually 50 to 98 per cent of the monomeric material is polymerized.

In preparing synthetic rubber by polymerizing conjugated dienes by theprocess of the invention, it is usually desirable to use apolymerization modifying agent, as is usually true in otherpolymerizations to produce synthetic rubber. Preferred polymerizationmodifiers for use in the process of the present invention are alkylmercaptans, and these may be of primary, secondary, or tertiaryconfigurations, and generally range from C3 to C16 compounds, but mayhave more or fewer carbon atoms per molecule. Mixtures or blends ofmercaptans are also frequently considered desirable and in many casesare preferred to the pure compounds. The amount of mercaptan employedwill vary, depending upon the particular compound or blend chosen, theoperating temperature, and the results desired. In general, the greatermodification is obtained when operating at relatively low temperaturesand therefore a smaller amount of mercaptan is added to yield a productof a given Mooney value, than is used at higher temperatures. In thecase of tertiary mercaptans, such as tertiary C12 mercaptans, blends oftertiary C12, C14, and C16 mercaptans, and the like, satisfactorymodification is obtained with 0.05 to 0.3 part mercaptan per 100 partsmonomers, but smaller or larger amounts can be employed in someinstances. In fact, amounts as large as 2.0 parts per 100 parts ofmonomers are sometimes used. Thus the amount of mercaptan is adjusted tosuit the case at hand.

Advantages of this invention are illustrated by the following examples.The reactants, and their proportions, and the other specific ingredientsof the recipes are presented as being typical and should not beconstrued to limit the invention unduly.

Example I The following recipe was employed for carrying out abutadiene-styrene copolymerization at 5 0.:

Parts by weight Butadiene '70 Styrene 30 Water 200 Fatty acid soap,potassium salt 5 Mercaptan blend 0.2 Potassium cyanate, KCNO VariableTriisopropylbenzene hydroperoxide Variable Potassium hydroxide -sVariable 1 Potassium Ofiice Rubber Reserve soap. A blend of tertiary C Cand C aliphatic mercaptans in a ratio of 3 1 1 parts y weight.

The following results were obtained:

The copolymerization of butadiene with styrene was effected according tothe following recipe using different oxidants:

Parts by weight Butadiene Styrene 30 Water Methanol 30 Fatty acid soap,5

K salt Mercaptan blend 0.2

KCNO, parts 0.162 (2 millimols) Oxidant (2.2 millimols) KOI-I 0.0 or0.112 (0 or 2 millimols) 1 As in Example I.

Polymerizations were started at 10 C. and allowed to continue for 29hours. Judging from the appearance of the emulsion, no reaction hadtaken place at the end of this period. The temperature was then raisedto +5 C. and held at this level. The following results were obtained(hours shown indicate total time at both temperatures) Conversion, KOHPercent Oxldant Parts 50.5 74.5 Hours Hours Hydrogen peroxide 0 0 0 Do0.112 0 0 Triisopropylbenzene hydroperoxide 0 5. 9 17.3 Do 0.112 15.126.0 Potassium persulfate 0 1. 2 3. 4 Do 0.112 2. 8 6. 8 0 0 0. 9

Potassium chlorate 0 0 0 Peracetic acid (neutralized with KOH)... 0 0.80.7 Do 0.112 1.2 1.1

7 These results'show that oxidants other than the hydroperoxide do notgive practical polymerization rates, and that temperatures below C. werenot operable, for this system.

Example III The following iron-free polymerization recipe was used:

Parts by weight Butadiene 70 Styrene 30 Water 200 Fatty acid soap, K

salt

Mercaptan blend 0.2

A blend of tertiary C C14. and C aliphatic mercap tans in a ratio of 3 11 parts by weight.

The following results were obtained:

Conversion, Percent 24.5 hours 98.6 hours Potassium cyanate, KCNO 23 70Potassium thiocyanate, KCNS 26 90 As will be evident to those skilled inthe art, various modifications of this invention can be made, orfollowed, in the light of the foregoing disclosure and discussion,without departing from the spirit or scope of the disclosure or from thescope of the claims.

I claim:

1. In the production of synthetic rubber by polymerization of amonomeric material comprising a conjugated diene having not more thansix carbon atoms per molecule while dispersed in an aqueous mediumcontaining an alkali metal fatty acid soap as an emulsifier in thepresence of a catalytic composition comprising an oxidant and areductant, the improvement which comprises polymerizing said monomericmaterial in the absence of more than traces of any heavy metal compoundand in the presence of a reductant comprising a compound having theformula MCNX where M represents a compound selected from the groupconsisting of the alkali metals and ammonium and X represents a compoundselected from the group consisting of oxygen and sulfur, together with amaterial which acts as an oxidant in the presence of said compound underthe conditions of polymerization.

2. In a process for the polymerization of a monomeric materialcomprising an organic compound having an active CH2=C group atpolymerization conditions while dispersed in an aqueous mediumcontaining an alkali metal fatty acid soap as an emulsifier in thepresence of a catalyst composition comprising an oxidant and areductant, the improvement which comprises using as said reductant acompound having the formula MCNX where M represents a compound selectedfrom the group consisting of the alkali metals and ammonium and Xrepresents a compound selected from the group consisting of oxygen andsulfur, together with a material which acts as an oxidant in thepresence of said com pound under the conditions of polymerization.

3. A process according to claim 2 wherein said reductant is potassiumthiocyanate.

4. A process according to claim 2 wherein said reductant is potassiumcyanate.

5. A process according to claim 2 wherein said reductant is sodiumcyanate.

6. A process according to claim 2 wherein said reductant is sodiumthiocyanate.

7. A process according to claim 2 wherein said reductant is ammoniumthiocyanate.

8. A process for producing synthetic rubber which comprises establishingand maintaining at a polymerization temperature of at least 0 C. anemulsion of an aqueous phase, a liquid monomeric material comprising amajor amount of 1,3-butadiene and a minor amount of styrene, an alkalimetal fatty acid soap as an emulsifying agent, a reaction modifier, anorganic hydroperoxide oxidant, and a compound having the formula MCNXwhere M represents a compound selected from the group consisting of thealkali metals and ammonium and X represents a compound selected from thegroup consisting of oxygen and sulfur.

9. In the polymerization of a monomeric material comprising an organiccompound having an active CH2=C group at a polymerization temperaturewhile dispersed in an aqueous medium in the presence of a trisubstitutedhydroperoxymethane oxidant, an alkali metal fatty acid coap as anemulsifier, and a reductant, the improvement which comprises using assaid reductant 0.02 to 2 parts of an alkali metal thiocyanate, saidamounts being per parts by weight of said monomeric material.

10. A process according to claim 9 wherein said monomeric materialcomprises a major amount of 1,3-butadiene and a minor amount of styrene.

11. In the polymerization of a monomeric material comprising an organiccompound having an active CH2:C group at a polymerization temperaturewhile dispersed in an aqueous medium in the presence of an oxidant, analkali metal fatty acid soap as an emulsifier, and a reductant, theimprovement which com-prises using as said reductant 0.02 to 2 parts ofa compound having the formula MCNX where M represents a compoundselected from the group consisting of the alkali metals and. ammoniumand X represents a compound selected from the group consisting of oxygenand sulfur, and using as said oxidant .25 to 10 millimols of atrisubstituted hydroperoxymethane, said amounts being per 100 parts byweight of said monomeric material.

12. A process according to claim 11 wherein said aqueous medium ismaintained at a pH of at least 9.

13. A process accordingto claim 12 wherein said pH is within the rangeof 9 to 12, and said reductant is an alkali metal thiocyanate.

14. A process according to claim 13 wherein said cyanate is KCNS, andsaid trisubstituted hydroxyperoxymethane is tert-butylisopropylbenzenehydroperoxide.

15. A process which comprises establishing and maintaining at apolymerization temperature between 0 and 30 C. an emulsion of an aqueousphase, a liquid monomeric material comprising an organic compound havingan active CH=C group, an alkali metal fatty acid soap as an emulsifyingagent, an organic hydroperoxide oxidant, and 0.02 to 2 parts, per 100parts by weight of said monomeric material, of a compound having theformula MCNX Where M represents a compound selected from the roupconsistin of the alkali metals and ammonium and X represents a compoundselected from the group consisting of oxygen and sulfur.

16. A process for producing synthetic rubber which comprisesestablishing and maintaining at a polymerization temperature between 0and 30 C. an emulsion of an aqueous phase having a pH of at least 9, aliquid monomeric material comprising a major amount of LS-butadiene anda minor amount of styrene, an alkali metal fatty acid soap as anemulsifying agent, a mercaptan reaction modifier, from 0.25 to 10millirnols of a organic hydroperoxidic oxidant, and from 0.02 to 2 partsof potassium cyanate, said amounts being per 100 parts by weight of saidmonomeric material.

1'7. A process for producing synthetic rubber.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,416,461 Stewart Feb. 25, 1947 2,486,943 Hammer et a1 Nov. 1,1949 2,527,393 Brown Oct. 24, 1950 2,537,642

Bebb Jan. 9, 1951

1. IN THE PRODUCTION OF SYNTHETIC RUBBER BY POLYMERIZATION OF AMONOMERIC MATERIAL COMPRISING A CONJUGATED DIENE HAVING NOT MORE THANSIX CARBON ATOMS PER MOLECULE WHICH DISPERSED IN AN AQUEOUS MEDIUMCONTAINING AN ALKALI METAL FATTY ACID SOAP AS AN EMULSIFIER IN THEPRESENCE OF A CATALYTIC COMPOSITION COMPRISING AN OXIDANT AND AREDUCTANT, THE IMPROVEMENT WHICH COMPRISES POLYMERIZING SAID MONOMERICMATERIAL IN THE ABSENCE OF MORE THAN TRACES OF ANY HEAVY METAL COMPOUNDAND IN THE PRESENCE OF A REDUCTANT COMPRISING A COMPOUND HAVING THEFORMULA MCNX WHERE M REPRESENTS A COMPOUND SELECTED FROM THE GROUPCONSISTING OF THE ALKALI METALS AND AMMONIUM AND X REPRESENTS A COMPOUNDSELECTED FROM THE GROUP CONSISTING OF OXYGEN AND SULFUR, TOGETHR WITH AMATERIAL WHICH ACTS AS AN OXIDANT IN THE PRESENCE OF SAID COMPOUND UNDERTHE CONDITIONS OF POLYMERIZATION.